This invention relates generally to a system for measuring physical characteristics of the body by a non-invasive and atraumatic process and apparatus and, more specially, to a method and apparatus for measuring water in the body by measuring certain electrical characteristics of the body by means of a four-electrode bridge or phase sensitive potentiometer technique.
In renal dialysis of a patient, it is important to know the effects that the dialysis procedure is having on the patient and to know the ultimate result of the dialysis procedure upon completion of the procedure. In view of the variations of weight from one patient to another, in order to properly evaluate the progression of the dialysis and the ultimate result of the dialysis, the starting weight and final weight of the patient must be known. Accordingly, in order to obtain these figures for comparison, it has been necessary to weigh the patient to determine a starting weight, a progression of loss of body weight, and an ultimate body weight after the completion of the dialysis. Thus, constant body weights must be taken before, during and after the dialysis to ascertain the benefits of the dialysis and a continuous control of weight loss is recommended. However, it has been found that the percentage of weight loss to total body weight during the renal dialysis procedure is an extremely small figure. Accordingly, this is not an accurate method of determining the benefits of the dialysis.
Further, prior procedures have included chemical tests which have been performed to determined specific blood chemistry or enzyme activity. This procedure requires blood samples to be taken from the patient, even though some patients are already suffering from an anemia condition. Also, this has not been found to be a satisfactory solution in view of the fact that there is not a continuous monitoring of the chemistry or enzyme activity nor are the results of sufficient accuracy to determine the benefits of the renal dialysis procedure.
The system of the present invention proposes an all electrical approach to the quantitative evaluation of the loss of body water relative to the total body weight to evaluate the reduction of body water or the planned stability of weight during the dialysis procedure. With the proposed system of the present invention, the physician may measure, with accuracy, the loss in body water or the lack of loss of water in the situation where certain molecules are being removed (as in the toxic patient) by measurement of certain impedance characteristics of the body by means of a intermediate radio frequency electrical signal which may be used to continuously monitor the patient. The method of the present invention is quantitative in the results provided and is non-invasive to the patient in that samples of body fluids are not removed from the patient for analysis. Further, it has been found that the percentage change in certain of the electrical characteristics measured by the system of the present invention provide a greater percentage change per unit of body water lost than heretofore known methods of determining body water loss.
Accordingly, it is one object of the present invention to provide an improved system for measuring the loss of body water or the control of body mass.
It is another object of the present invention to provide an improved system for measuring the loss of body fluid by use of electrical apparatus for measuring the mutual impedance of portions of the body of a patient.
It is another object of the present invention to provide an improved system for measuring the loss of body fluid of a portion or the entirety of the human body by comparing an electrical characteristic of the body taken before the water loss to the same electrical characteristic taken after the water loss.
It is still another object of the present invention to provide an improved electrical characteristic measuring system for determining the effectiveness of renal dialysis which measures the electrical characteristics having the greatest percentage change per loss of body water.
It is still another object of the present invention to provide an improved system for electrically measuring characteristics of the body indicative of the loss of body water during renal dialysis and particularly which measure the capacitive reactance and impedance angle of the body.
It is still another object of the present invention to provide an improved electrical system for measuring characteristics of the body representative of body water loss during renal dialysis which includes a four-electrode system for providing inputs to a vector voltmeter type of measuring instrument.
It is still a further object of the present invention to provide an improved system for measuring bio-electrical impedance during renal dialysis.
It is still another object of the present invention to provide an improved system for measuring the effects of renal dialysis which is continuous, quantitative and non-invasive.
It is still a further object of the present invention to provide an improved system for measuring the effects of renal dialysis which is simple to use and reliable in operation.